1. Field of the Invention
The present invention generally relates to a method of manufacturing a semiconductor device including the step of forming a silicon oxynitride film on a silicon substrate, and more particularly to a method of localizing nitrogen at an interface between the silicon substrate and the silicon oxynitride film. The present invention also relates to a semiconductor device obtained by such methods.
2. Description of the Background Art
The method of forming a silicon oxynitride film as a gate insulating film on a silicon substrate is conventionally known. The silicon oxynitride film as a gate insulating film is used because the reliability of an insulating film and therefore a device increases compared with a silicon oxide film.
The method of forming a silicon oxynitride film is described in Appl. Phys. Lett. 63 (1993), p. 54, for example. Here, a silicon oxynitride film is formed by using N.sub.2 O gas and an RTA device (Rapid Thermal Anneal device). Meanwhile, it is known that an oxynitride film formed by an older prior art diffusion furnace has nitrogen diffused to the entire film.
However, any of the conventional methods was not designed for intentionally controlling the depth direction profile of nitrogen in an oxynitride film. Therefore, a method in which TDDB (Time Dependent Directric Breakdown) characteristics are sufficiently satisfied has not been obtained. That is, when a silicon oxynitride film obtained by a conventional method is used as a gate insulating film, the silicon substrate and the gate electrode are electrically connected.